Foils and moldings composed of cycloolefin copolymers (COC) exhibit low density, high transparency, low birefringence, extremely low water absorption and high stiffness, strength and hardness.
Processing of COC on conventional industrial extrusion plants to make foils or films, e.g. on grooved- or smooth-barrel extruders, often leads to an increased number of defects in the foil, such as gelling or fish eyes. The increased defect numbers restrict the usefulness of the material for certain industrial applications. Other polymers which may be processed into foils with lower occurrence of defects, do not however, have the excellent properties of the cycloolefin copolymers, in particular high stiffness. There is therefore a need for foils, or moldings, with minimum defects, which generally have the properties of the cycloolefin copolymers. For the purposes of this application, the term foil also means film or sheet.
EP 384 694 A describes the production of films composed of blends of COC and of other polymers, e.g. of polyolefins. The films thus obtained generally have good surface properties, but there is no further description of the individual properties. Nor does the document give any indication of the reduction in the defect numbers during production of films.
It was an object of the present invention to provide polymers which permit production of foils or moldings with reduced occurrence of defects.